For many years vendors of reproducible media have been concerned with unauthorized duplication of media products such as music recordings, computer software, and published works, to name several. Early software producers employed anti-copy techniques including “bad sectoring” which employed a corrupt segment in a delivered original. More recently, validation codes have been employed to register a machine specific hash with a particular installation of an operating system to ensure each delivered copy of physical media was installable on a single machine. Movie producers at one time feared that home video recorders would cause the demise of the motion picture industry, and began generating “uncopyable” tapes which would play acceptably but not generate a recordable signal for other machines to copy.
Mechanisms evolved to identify unauthorized or undesired propagation and distribution of media items. The study of steganography encompasses the practice of hidden or obscured messages in printed and visible works, and includes outright cryptography and other ciphers which render the media unintelligible. Unlike cryptography, however, steganographic techniques in general do not necessarily obliterate the underlying media item, and therefore does not draw attention the way encryption does. Therefore, while steganographic implementations may inject either readily visible or more obscured artifacts in the underlying media item, they generally do not prohibit intelligible reception by the user, but rather continue to merely denote the source or origin of the media item.